How to use multiple objects and their methods from multiple classes

Question

I have three classes. I want to use all classes in one function from another classes. I need to collect all Letter class objects and put the result from getName and getWeight from each object in a HashMap. I need to this with Package and Deliverer as well.

Already tried to use getDeclaredField/getDeclaredClasses.

import java.lang.reflect.Field;

public class Parcel
{
    protected static void addWeight()
    {
        Class<?>[] classes = Letter.class.getDeclaredClasses();
        for (int i = 0; i < classes.length; i++) {
            System.out.println("hello");
            System.out.println("Class = " + classes[i].getName());
        }

        Field[] allFieldsLetter = Letter.class.getDeclaredFields();
        for (int i = 0; i < allFieldsLetter.length; i++) {
            double value = Letter.getWeight();
            Delivery.weightList.put(Letter.getName(), value);
        }
        Field[] allFieldsPackage = Package.class.getDeclaredFields();
        for (int i = 0; i < allFieldsPackage.length; i++) {
            double value = Package.getWeight();
            Delivery.weightList.put(Package.getName(), value);
        }
        Field[] allFieldsDeliverer = Deliverer.class.getDeclaredFields();
        for (int i = 0; i < allFieldsDeliverer.length; i++) {
            double value = Deliverer.getWeight() * 5;
            Delivery.deliverer.put(Deliverer.getName(), value);
        }
    }
}

If I create 3 Deliverer objects for example, I want to get 3 three names, one for each object, and their weights in a HashMap (Delivery.deliverer.put(Deliverer.getName(), value);).

Your code doesn't make much sense, you are using for loops but you are not accessing values from any array or any other type of collection inside them and you talk about having 3 objects of a type but all your code uses static methods and variables. Is the hashmap supposed to be a static instance for each class or a member variable or perhaps a global collection for all object types? — Joakim Danielson
– Joakim Danielson, Commented Oct 29, 2019 at 12:31
I don't think you mean to be using the reflective classes/methods for class and fields. Your comments suggest you mean to be doing something much more normal like creating list of objects and then looping over them. I'm I on the right track? — fedup
– fedup, Commented Oct 29, 2019 at 13:21

fedup · Accepted Answer · 2019-10-29 13:29:24Z

1

Here is a small example where Delivery has a constructor that accepts the name and the value of weight as a parameter.

List<Delivery> myDeliveryInstances = new ArrayList<Delivery>();

myDeliveryInstances.add(new Delivery("D1", 10));
myDeliveryInstances.add(new Delivery("D2", 25));
myDeliveryInstances.add(new Delivery("D3", 50));

Map<String, Long) deliverer = new HashMap<String, Long>();
for (Delivery delivery : myDeliveryInstances) {
    deliverer.put(delivery.getName(), delivery.getWeight());
}

answered Oct 29, 2019 at 13:29

fedup

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1 Comment

Ties Over a year ago

When I get home will try this solution, seems to be a pretty good one ;)

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